Steve Connor: We may be on the brink of major instability

Decent science fiction has more than a grain of truth to it. So it was with The Day After Tomorrow, the movie that brought the esoteric science of ocean currents to cinema audiences. But the fantastical plot behind the film contained only a tiny grain of truth in a whole sackful of Hollywood hype.

As anyone who has done basic geography should know, we in Britain live at the same latitude as Newfoundland, yet we enjoy a much milder climate thanks to the heat brought to us by the Gulf Stream, or more accurately, the North Atlantic Drift. Newfoundland, meanwhile, bathes in the icy Labrador Current. It is estimated the Gulf Stream's heat content is equivalent to the output of about a million power stations.

If this vital ocean current were to slow down or shut off completely, we would feel a lot colder in winter, with our ports and shores icing up as they do in Newfoundland. The pump that drives this ocean current, or at least a major part of it, is known as the thermohaline circulation. This ocean current is dependent on both heat and the salinity of sea water, so anything that affects either has the potential to upset the pump that moderates our climate.

About 13,000 years ago, after the last ice age, it was thought that this actually happened when a huge volume of fresh water flowed relatively quickly from the melting ice sheet of North America into the North Atlantic. It is thought that the sudden flow of huge volumes of fresh water disturbed the salty pump behind the warm ocean currents of the North Atlantic.

What is going on now in the Arctic appears to be small beer by comparison. The volumes of fresh water building up on the surface of the Arctic Ocean are tiny compared with the really massive amounts of meltwater that flowed from the ancient glacial Lake Agassiz of North America, which is estimated to have contained more fresh water than all the lakes of the world combined.

Yet, from what the experts are telling us, there is some cause for concern. We may be witnessing a further climatic change in the Arctic that could become unstable. It needs to be monitored closely if we are to understand its significance.